The goal of this study is to determine structure/function relationships among single neurons in laminae 4, 5 and 6 of cat striate cortex (area 17). Cells will be recorded extra- and intracellularly using micropipetes filled with horseradish peroxidase (HRP). Each cell's visual receptive field properties and major functional class will be determined. Where possible, electrical stimulation will also be used to determine 1) the affarent drive to a cell from Y, X or W relay neurons of the dorsal lateral geniculate nucleus (LGNd), and 2) the cell's subcortical projection sites. HRP will then be iontophoresed into the cell, allowing subsequent light microscopic examination of the cell's complete morphology. The major aims are to fully characterize the morphological cell types (i.e., spinous/aspinous stellate and pyramidal cells) in each of these layers and to determine what receptive field class or classes are associated with each structural type. I will also search for correlations between single receptive field properties (viz., field size, orientation tuning or velocity sensitivity) and structural features (viz., size and laminar locations of cells' dendritic and axonal arbors) of the cells. Relationships between the type of LGNd input (Y, X or W) to a cell and the cell's interlaminar dendritic and axon projections will be examined. Finally, for many efferent cells in layer 5 or 6, I will determine whether cells which project to different subcortical sites also differ in their detailed morphology. The results of this study will provide basic information on normal structure/function relationships among area 17 neurons. Insights will also be provided into how information from the LGNd is channelled into, through, and out of the visual cortex. This study is the first phase of a long-term investigation of the cellular bases of information processing in visual cortex.